Your friend is the more natural, spontaneous person in this friendship, and you'll both feel an increasing amount of tension as a result. They will come to feel as if they have to suppress their natural self-expression, which will be a bit depressing for them; it may even chip away at their self-esteem, because your reaction may translate to them as disapproval or even distaste. That's not what's going on, of course; for you, it's be more about needing to feel secure before you can start relaxing into a more natural, spontaneous ways of expressing yourself.
But the day-to-day reality of your friendship may blow hot and cold. Sometimes you'll feel like there's a barrier between you that even the best of intentions can't cross. If you decide to, you'll be able to work on this together and become more trusting and in sync over time.